April2018

OSPF LSA5 forwarding address

Did you know that OSPF can redistribute routes with their original next-hop addresses?

In the topology above, the leftmost router (lets call it router 1) injects network 172.16.1.0/24 into EIGRP. ASBR redistributes to OSPF. ASBR will as we now create a type5 LSA for the external type network. But did you know that it can preserve the original next-hop address from EIGRP?  The feature is called “OSPF Type 5 LSA forwarding address feature” and lets us preserve the next-hop address in some topologies in order to spare one unnecessary hop.

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